U.S. patent number 5,138,659 [Application Number 07/694,796] was granted by the patent office on 1992-08-11 for conversion of television signal formats with retention of common control data stream.
This patent grant is currently assigned to General Instrument Corporation. Invention is credited to Christopher J. Bennett, Kris Kelkar.
United States Patent |
5,138,659 |
Kelkar , et al. |
August 11, 1992 |
Conversion of television signal formats with retention of common
control data stream
Abstract
Television signals are converted from a first format to a
plurality of different formats while retaining a common control
data stream. A first television signal in a first format is
separated into a first signal portion carrying television
information and a second signal portion carrying control data. The
first signal portion is reformatted into a second format. The
second signal portion is combined with the reformatted first signal
portion to provide a second television signal. In this manner, a
plurality of television signals having different formats can be
transmitted with common control data, e.g., for controlling access
to television programming.
Inventors: |
Kelkar; Kris (San Diego,
CA), Bennett; Christopher J. (San Diego, CA) |
Assignee: |
General Instrument Corporation
(Hatboro, PA)
|
Family
ID: |
24790316 |
Appl.
No.: |
07/694,796 |
Filed: |
May 2, 1991 |
Current U.S.
Class: |
380/239;
348/E7.055; 348/E7.024; 348/441; 380/210; 348/443; 375/E7.001 |
Current CPC
Class: |
H04N
7/08 (20130101); H04N 7/24 (20130101); H04N
7/167 (20130101) |
Current International
Class: |
H04N
7/08 (20060101); H04N 7/24 (20060101); H04N
7/167 (20060101); H04N 007/167 () |
Field of
Search: |
;380/20
;358/141,140 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Brochure--Philips BSB Satellite Receiver Model STU902. .
Brochure--CEL Electronics Ltd. Model P156-2 Television Standards
Converter. .
Brochure--Video International Model DTC 1504 Television Standards
Converter..
|
Primary Examiner: Tarcza; Thomas H.
Assistant Examiner: Cain; David
Attorney, Agent or Firm: Lipsitz; Barry R.
Claims
What is claimed is:
1. A method for converting television signals to provide a
plurality of different television formats while retaining a common
control data stream among the different formats comprising the
steps of:
separating a first television signal in a first television format
into a first signal portion carrying television information and a
second signal portion carrying control data;
reformatting said first signal portion into a second television
format; and
combining said second signal portion with said reformatted first
signal portion to provide a second television signal;
whereby said first and second television signals have different
television formats but contain common control data.
2. A method in accordance with claim 1 comprising the further step
of concurrently transmitting said first and second television
signals.
3. A method in accordance with claim 1 comprising the further step
of descrambling said first signal portion before said reformatting
step.
4. A method in accordance with claim 3 comprising the further step
of rescrambling said first signal portion after said descrambling
step in a manner compatible with said second format.
5. A method in accordance with claim 4 comprising the further step
of deriving secret information from said first television signal
for use in descrambling and rescrambling said first signal
portion.
6. A method in accordance with claim 4 comprising the further steps
of decrypting and reencrypting said second signal portion before
said combining step in a manner compatible with said second
format.
7. A method in accordance with claim 6 comprising the further step
of deriving secret information from said first television signal
for use in descrambling and rescrambling said first signal portion
and for use in decrypting and reencrypting said second signal
portion.
8. A method in accordance with claim 1 comprising the further steps
of decrypting and reencrypting said second signal portion before
said combining step in a manner compatible with said second
format.
9. A method in accordance with claim 8 comprising the further step
of deriving secret information from said first television signal
for use in decrypting and reencrypting said second signal
portion.
10. A method in accordance with claim 1 wherein said common control
data provides access control for said first and second television
signals at corresponding television signal decoders.
11. A method in accordance with claim 1 wherein said first format
is one of a MAC, PAL, SECAM, NTSC and HDTV television format and
said second format is another of said MAC, PAL, SECAM, NTSC and
HDTV television formats.
12. A method in accordance with claim 1 comprising the further
steps of:
reformatting said first signal portion into at least one additional
format; and
combining said second signal portion with said additional
reformatted first signal portion to provide at least one additional
television signal;
whereby said first, second and additional television signals all
contain common control data.
13. A method in accordance with claim 12 comprising the further
step of concurrently transmitting said first, second and additional
television signals.
14. A method in accordance with claim 1 comprising the further step
of filtering said second signal portion before said combining step
to delete a portion of said control data.
15. Apparatus for converting television signals to provide a
plurality of different television formats while retaining a common
control data stream among the different formats comprising:
means for separating a first television signal in a first
television format into a first signal portion carrying television
information and a second signal portion carrying control data;
means coupled to an output of said separating means for
reformatting said first signal portion into a second television
format; and
means coupled to an output of said reformatting means for combining
said second signal portion with said reformatted first signal
portion to provide a second television signal;
whereby said first and second television signals have different
television formats but contain common control data.
16. Apparatus in accordance with claim 15 further comprising:
means for concurrently transmitting said first and second
television signals to a plurality of decoders responsive to said
common control data.
17. Apparatus in accordance with claim 15 further comprising: means
coupled between said separating and reformatting means for
descrambling said first signal portion.
18. Apparatus in accordance with claim 17 further comprising: means
operatively associated with said reformatting means for
rescrambling said first signal portion in a manner compatible with
said second format.
19. Apparatus in accordance with claim 18 further comprising: means
for deriving secret information from said first television signal
for use in descrambling and rescrambling said first signal
portion.
20. Apparatus in accordance with claim 18 further comprising: means
coupled between said separating and combining means for decrypting
and reencrypting said second signal portion in a manner compatible
with said second format.
21. Apparatus in accordance with claim 20 further comprising: means
for deriving secret information from said first television signal
for use in descrambling and rescrambling said first signal portion
and for use in decrypting and reencrypting said second signal
portion.
22. Apparatus in accordance with claim 15 further comprising: means
coupled between said separating and combining means for decrypting
and reencrypting said second signal portion in a manner compatible
with said second format.
23. Apparatus in accordance with claim 22 further comprising: means
for deriving secret information from said first television signal
for use in decrypting and reencrypting said second signal
portion.
24. Apparatus in accordance with claim 15 wherein said common
control data provides access control for said first and second
television signals at corresponding television signal decoders.
25. Apparatus in accordance with claim 15 wherein said first format
is one of a MAC, PAL, SECAM, NTSC and HDTV television format and
said second format is another of said MAC, PAL, SECAM, NTSC and
HDTV television formats.
26. Apparatus in accordance with claim 15 further comprising:
means for reformatting said first signal portion into at least one
additional format; and
means for combining said second signal portion with said additional
reformatted first signal portion to provide at least one additional
television signal;
whereby said first, second and additional television signals all
contain common control data.
27. Apparatus in accordance with claim 26 further comprising: means
for concurrently transmitting said first, second and additional
television signals to a plurality of decoders responsive to said
common control data for providing or denying access to said first
signal portion.
28. Apparatus in accordance with claim 15 further comprising means,
coupled between said separating and combining means, for filtering
said second signal portion to remove a portion of said control
data.
29. Apparatus in accordance with claim 15 wherein said reformatting
means convert color information in said first signal portion into a
different format.
30. Apparatus in accordance with claim 15 wherein said reformatting
means convert a line rate of said first signal to a different line
rate.
Description
BACKGROUND OF THE INVENTION
The present invention relates to television signal distribution,
and more particularly to a method and apparatus for converting
between different television signal formats while retaining a
common control data stream.
Television signals are conventionally transmitted in analog form
according to various standards adopted by particular countries. For
example, the United States has adopted the standards of the
National Television System Committee ("NTSC") while most European
countries have adopted either PAL (phase alternating line) or SECAM
standards. A family of multiplexed analog component ("MAC")
systems, in particular C-MAC, D2-MAC, and D-MAC have been proposed,
mainly for direct broadcast satellite service ("DBS") applications
wherein television signals are broadcast directly from a satellite
to an earth station operated by the end user. The various MAC
systems differ mainly in how the digitized sound is realized, and
all need more bandwidth than an NTSC signal. Entirely new color
television systems, not constrained by the limitations of the
systems noted above, may be developed for high definition
television ("HDTV"). The main attributes of HDTV are a new aspect
ratio of picture width to height, a substantially increased number
of scan lines for more vertical resolution, and a greater video
bandwidth for more horizontal resolution. Some proposed HDTV
systems achieve a bandwidth comparable to that for NTSC television
signals by using digital compression techniques.
The various television systems identified above are all
incompatible. Therefore, a programmer such as Home Box Office
("HBO") that desires to serve markets in which various standards
are used, must live with the added complexity of generating a
plurality of incompatible signal formats for communication via a
broadcast media such as satellite, cable, or terrestrial
transmission. Since programmers of premium television services must
control access to their signals in order to derive subscriber
revenues, an access control data stream is transmitted with the
television information to permit authorized subscribers to receive
particular programs via a descrambler. In the past, the different
television broadcast systems each used a different access control
data stream to enable authorized subscribers to receive particular
television programs. Thus, signal programmers must contend with
different access control schemes as well as different broadcast
formats. This requirement increases the complexity and cost of the
equipment required by a programmer.
Access control systems for television signals provided in a single
format are well known. One such system is disclosed in U.S. Pat.
No. 4,613,901 to Gilhousen, et al entitled "Signal Encryption and
Distribution System for Controlling Scrambling and Selective Remote
Descrambling of Television Signals", incorporated herein by
reference. In the Gilhousen, et al system, a unique encryption key
stream is generated for scrambling a television signal. The
scrambled television signal is transmitted together with control
data including various cryptographic keys. At each descrambler
authorized to receive a particular television signal, the
encryption key stream is reproduced for use in descrambling the
television signal.
Other selective subscription descrambling systems are disclosed in
Gilhousen, et al U.S. Pat. Nos. 4,712,238 and 4,792,973. These
patents provide improved systems for enabling descrambling of a
received scrambled signal on an impulse-purchase basis. U.S. Pat.
No. 4,634,808 to Moerder discloses a system for reproducing a key
signal in a descrambler that is unique to the descrambler, and was
used in encrypting a key signal that must be decrypted for use in
descrambling a television signal.
It would be advantageous to provide a system for converting
television signals of one format to one or more other formats while
maintaining a common control data stream among the different
formats. This would enable simplification of a television signal
distribution system, by permitting the same hardware and software
to be used to provide access control for television signals
broadcast in any format.
The present invention provides a system having the aforementioned
advantages.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method and apparatus
are provided for converting television signals to provide a
plurality of signal formats while retaining a common control data
stream among the different formats. A first television signal in a
first format is separated into a first signal portion carrying
television information and a second signal portion carrying control
data. The first signal portion is reformatted into a second format.
The second signal portion is combined with the reformatted first
signal portion to provide a second television signal. In this
manner, the first and second television signals contain common
control data.
By concurrently transmitting the first and second television
signals, access to television programs by receivers operating in
either the first or second format is provided. The common control
data provides or denies access to particular television programs
regardless of the television format in which the program signals
are received. Authorized subscribers will be permitted to view a
particular program, and access by unauthorized subscribers will be
denied.
In an illustrated embodiment, the first signal portion of the first
television signal is descrambled before it is reformatted into the
second format. The first signal portion can be rescrambled after
descrambling in a manner compatible with the second format.
The first format in which a television signal is broadcast can be,
for example, any of the MAC, PAL, SECAM, NTSC, and HDTV television
formats. The second format can be another of said MAC, PAL, SECAM,
NTSC, and HDTV television formats.
In accordance with an expanded embodiment of the present invention,
the first signal portion of the first television signal is
reformatted into at least one additional format. The second signal
portion is combined with the additional reformatted first signal
portion to provide at least one additional television signal. In
this manner, a television signal in a first format can be provided
in any number of different formats all containing common control
data.
In an illustrated embodiment, secret information is derived from
the first television signal for use in descrambling and
rescrambling said first signal portion. Where the second signal
portion is transmitted in an encrypted form, it can be decrypted
and reencrypted in a manner compatible with the second format
before it is combined with the reformatted first signal portion.
Secret information derived from the first television signal can
also be used in connection with the decryption and reencryption of
the second signal portion.
In the present disclosure, the terms "descrambling" and
"rescrambling" are used in connection with the television
information portions (i.e., video and audio) of a television
signal. It should be appreciated that the video and audio
information can be provided in either an analog or digital format.
For example, satellite television signals are conventionally
transmitted with analog video and digital audio. HDTV signals, on
the other hand, are expected to be fully digital in nature.
The terms "decrypting" and "encrypting" are used herein in
connection with the control data portions of a signal, which are in
digital form.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a general embodiment of the present
invention illustrating the conversion of television signals in one
format to another format while retaining a common control data
stream among the different formats;
FIG. 2 is a block diagram of a specific embodiment in which
television signals in a MAC format are converted to a PAL format;
and
FIG. 3 is a block diagram of an alternate embodiment wherein
television signals in a first format are converted to a plurality
of different formats, all retaining a common control data
stream.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a method and apparatus for
converting a television signal containing a digital access control
data stream from one format to another, while preserving all or
part of the access control data stream. The term "format" as used
herein refers to modulating and encoding formats such as those used
in broadcasting NTSC, PAL, SECAM, MAC, and HDTV television signals.
Typically, the digital access control data stream is an addressable
data stream that has been modulated into the television waveform
for purposes of implementing a conditional access control system
that limits access to programming. It should be appreciated that
the invention is also applicable to other types of data streams,
and is not limited solely to television program access control.
FIG. 1 is a general block diagram of apparatus in accordance with
the present invention. A television signal in a first format is
input at terminal 10, and contains in addition to its video and
audio components, a digital access control data stream that is
modulated in the television signal using a modulation scheme that
does not violate the specifications of the first format. In
addition to the video and audio components, which include video
luminescence, video chrominance, and one or more audio channels,
the television signal can also include auxiliary data or video
helper signals containing temporal information, frequency
information, or panels of the video signal. The apparatus
illustrated in FIG. 1 converts the television signal from the first
format to an equivalent television signal in a second format. The
signal in the second format contains all or a portion of the
television information and all or a portion of the access control
data stream contained in the first format.
The television signal input at terminal 10 is coupled to a
demodulator 12 that is a conventional device for demodulating the
signal from a frequency suitable for transmission or an
intermediate frequency to a frequency that is more suitable for
processing. The demodulated signal is then input to a TV decoder 14
and a data demodulator/decoder 16. The TV decoder is a conventional
circuit that decodes the television signal in the first format into
its components (i.e., video components, audio components, auxiliary
data, and/or video helper signals). Decoder 14 is specifically
adapted to decode television signals in the first format.
Data demodulator/decoder 16 is a conventional circuit that extracts
the digital access control data stream contained in the television
signal in the first format. The particular data demodulator/decoder
used will be determined by the modulation format that modulates the
data into the television signal input at terminal 10. The
combination of demodulator 12, television decoder 14, and data
demodulator/decoder 16 separate the television signal input at
terminal 10 into a first signal portion carrying television
information and output from decoder 14, and a second signal portion
carrying control data and output from decoder 16.
The television information output from decoder 14 is input to a
descrambler 18. Descrambler 18 is a conventional descrambler that
descrambles any scrambled components contained in the television
signal input at terminal 10. As noted above, these components can
be either analog or digital signals. In order to perform the
descrambling, a control module 30 derives secret information (e.g.,
cryptographic keys) from data contained in the input television
signal, and communicates the secret information to the descrambler.
The information used by control module 30 to derive the secret
information can reside anywhere in the input television signal. If
the information resides in the television information portion of
the signal, it is decoded by television decoder 14 and passed to
data demodulator/decoder 16 via dashed line 15. Then, control
module 30 obtains the decoded information at the output of data
demodulator/decoder 16. If the data required to derive the secret
information is carried in the control data portion of the input
television signal, it is decoded directly by decoder 16 for input
to control module 30.
The descrambled television signal, still in the first format, is
output from descrambler 18 to a scrambler 20. Scrambler 20 is a
conventional scrambling circuit that rescrambles the television
components in a manner compatible with a second format to which the
television signal will be converted. Like descrambler 18, scrambler
20 operates on the basis of secret information received from
control module 30.
The rescrambled signal output from scrambler 20 is input to a
television encoder 22 that comprises a conventional circuit for
encoding all or a portion of the television components that were
originally transmitted in the first format into a second format.
Examples of commercially available television encoders are found in
the Philips BSB Satellite Receiver model STU902 that converts MAC
signals to PAL signals, the CEL Electronics Ltd. model P156-2
television standards converter that converts between SECAM/PAL and
NTSC signals, and the Video International model DTC 1504 television
standards converter that converts between PAL and NTSC.
Descrambler 18 and scrambler 20 are not necessary in all
embodiments of the present invention. In particular, where the
television signal input to terminal 10 is not scrambled,
descrambler 18 and scrambler 20 can be bypassed as indicated by
line 17. Alternatively, where the signal in the first format is not
scrambled, but the television signal in the second format is to be
scrambled, descrambler 18 can be eliminated while scrambler 20 is
provided in the signal conversion apparatus. Similarly, a
descrambler 18 can be provided without a scrambler 20.
Data demodulator/decoder 16 outputs the control data portion of the
input television signal. In the event the control data is encrypted
in a manner that is incompatible with the second format, a
decrypter 24 is provided to decrypt the digital access control data
stream. An encrypter 26 reencrypts the decrypted data from
decrypter 24 in a manner that is compatible with the second format.
Decrypter 24 and encrypter 26 receive secret information from
control module 30, in order to properly decrypt and encrypt the
data. The secret information is derived by control module 30 from
the input television signal as described above. In an embodiment
where neither of the first and second formats or only one of the
formats uses decrypted data, decrypter 24 and/or encrypter 26 can
be bypassed as illustrated at line 19.
The control data stream is input to data modulator/encoder 28, that
modulates the digital data stream into the television signal in
appropriate places in accordance with the requirements of the
second format. The resultant television signal in the second
format, including both video and audio components and the common
control data is then input to a remodulator 32. This device
modulates the television signal in the second format from the
frequency used in the conversion process to a frequency more
suitable for transmission or for interfacing to transmission
equipment. The remodulated signal is output on terminal 34.
FIG. 2 illustrates a specific embodiment of the present invention
for converting MAC formatted television signals to PAL formatted
television signals, while maintaining common control data between
the MAC and PAL versions. Television programs are encoded in the
MAC format with the addition of an access control data stream into
the MAC signal. This signal can be received and viewed by a
population of MAC receivers containing a conditional access control
system that utilizes the access control data stream. An example of
such an access control system is the VideoCipher II system marketed
by the VideoCipher Division of General Instrument Corporation, San
Diego, Calif., U.S.A.
The apparatus of FIG. 2 generates a PAL signal with the very same
conditional access information as the input MAC signal. This allows
a population of PAL receivers using the conditional access control
system to view programming that originated in the MAC format.
Furthermore, the apparatus in accordance with the present invention
allows a system operator to transmit the television programs
without any need to distinguish between PAL receivers and MAC
receivers in the distribution system. The operator can treat both
the PAL and MAC receiver population as a single population of
receivers using the same conditional access control system. By
providing a control system that is independent of the various
transmission formats, programmers are able to reach a larger
population of receivers using the same conditional access control
system.
A modulated MAC signal containing basic television components and
an access control stream is input to terminal 40 from a
terrestrial, satellite or cable distribution system. A MAC receiver
42 demodulates the signal to baseband MAC. A MAC decoder 44 then
extracts the components in the signal (which in this case include
luminance, chrominance, and audio) and the access control stream.
The access control stream is sent to an access control module 50,
that obtains and derives the information necessary for a MAC
descrambler 46 to convert the received television signal components
into clear, unscrambled television components. MAC descrambler 46
receives analog video components from MAC decoder 44 via line 43,
and receives digital audio components via line 45. The descrambled
components output from MAC descrambler 46 are input to a PAL
component encoder 52, that encodes them into a PAL waveform. The
PAL waveform is then scrambled by PAL scrambler 54 under control of
the control module 50. A data filter 48 can be provided to remove
MAC only authorizations and overhead information that is specific
to the MAC format. The access control stream is then modulated into
portions of the PAL waveform by a data encoder 56 and PAL scrambler
54. The resulting signal is remodulated in PAL modulator 58 and
transmitted to PAL receivers via terrestrial, satellite or cable
transmission systems coupled to output terminal 60.
FIG. 3 illustrates a multiple format conversion apparatus in
accordance with the present invention. A television signal in a
first format is input at terminal 70. Receiver 72 demodulates the
signal to baseband for output to a decoder 74. The demodulated
baseband signal is separated into a first signal portion carrying
television information and a second signal portion carrying control
data. The television information is input to each of a plurality of
reformatters 76, 78, 80. Each reformatter converts the television
information from the first format to a different format as
described in connection with FIGS. 1 and 2 above. Control module 82
provides the secret information necessary to enable reformatters
76, 78, 80 to descramble and/or scramble the television
information. Data processing circuitry 84 is equivalent to the data
filter 48 and data encoder 56 of FIG. 2.
The outputs of each of the reformatters comprise the television
information in different formats. The reformatted information from
each of reformatters 76, 78, 80 is input to a corresponding
multiplexer 86, 88, 90. These multiplexers combine the reformatted
television information with the common control data from data
processing circuitry 84. Output terminal 92 of multiplexer 86
contains the television information in one format together with the
common control data. Output terminal 94 of multiplexer 88 contains
the television information in another format together with the
common control data. Output terminal 96 of multiplexer N contains
the television information in yet another format combined with the
common control data. A television signal in a first format can be
converted to any number of additional formats in this manner, with
each format containing a common control data stream.
It should now be appreciated that the present invention provides a
method and apparatus for converting television signals from one
format to one or more different formats while preserving a digital
access control data stream for use with all of the formats. Each of
the output formats can contain all of the common control data, or
only the portions thereof necessary to authorize receivers for the
particular format. System operators and programmers that distribute
signals to subscribers having receivers that operate using the
different formats can use the same access control hardware and
software, even though the television information is transmitted in
a variety of different formats.
Although the invention has been described in connection with
various preferred embodiments, those skilled in the art will
appreciate that numerous adaptations and modifications may be made
thereto without departing from the spirit and scope of the
invention, as set forth in the following claims.
* * * * *